<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <input type="password">
    <button>显示密码</button>

    <script>
        let input = document.querySelector('input');
        let button = document.querySelector('button');
        button.onclick = function(){
            if (input.type == 'text') {
                input.type = 'password';
                button.innerHTML = '显示密码';
            } else if (input.type == 'password') {
                input.type = 'text';
                button.innerHTML == '隐藏密码';
            }
        }
    </script>
</body>
</html>